1. Field of the Invention
This invention is directed to systems and devices which are useful in, the improvement of hearing ability of an individual, in general, and, more particularly, to methods and apparatus for providing improvement in hearing and spatial processing of sound by improving the discernment of sound in the "perceptual space" of the individual.
2. Prior Art
It is currently recognized by the public at large that hearing impairment is a serious problem. However, this problem has, generally, not received the same attention as other diseases, maladies or impairments. Typically, the reason for the lack of attention is that hearing impairment is the "silent handicap". That is, it is not as readily apparent to the public as are other physical handicaps. In fact, many hearing impaired individuals are unaware of their loss until tested or confronted with a specialized circumstance. Nevertheless, impaired hearing can have a significant impact on the quality of life of the individual involved. Therefore, it has been a source of investigation by many researchers (of various levels of ability) over the years to produce hearing enhancements or "hearing aids". These "aids" are available at various levels of technical expertise.
One type of hearing aid available on the market uses noise supression techniques. However, conventional filtering techniques generally are not considered to be effective or adequate for providing truly high fidelity frequency compensation which is desirable in hearing aids. Thus, results from implementation of these techniques often suffer from muffled sound outputs, as well as unacceptable noise and ringing problems.
A further problem in the conventional design of hearing aids is the inadequate treatment of background noise. Thus, a related problem with conventional hearing aid design is that the user will normally reduce the volume to reduce the higher intensity energy produced, for example, by vowels. However, at the same time the user sacrifices speech intelligibility by simultaneously reducing the intensity of the lower energy signals, e.g., sounds produced by consonants. Further, hearing aids which employ automatic gain control (i.e., gain decreases as input level increases) have the disadvantage of decreasing the gain as a function not only of the lower frequency, stronger vowel sounds contained in speech but also by the large energy, low frequency background noises. Because background noise and vowels can have the same effect on the gain control, an abnormal relationship between speech sounds is introduced. High frequency consonants, for example, are not amplified sufficiently in the presence of background noises thereby resulting in greatly reduced speech intelligence. In conventional hearing aid systems all sounds are amplified whereupon background noises greatly mask speech intelligibility.
It is well known from Bekesy's model of the ear that predominantly low frequency noise masks the higher frequency consonants because of the travelling wave phenomenon of the basilar membrane. Thus, low frequency information masks high frequency information. However, the reverse is not true. This phenomenon is commonly referred to in the literature as the "upward spread" of masking.
A particularly troublesome area for the hearing impaired individual occurs during normal conversation in an environment of a conference or large office. Persons with normal hearing are able to selectively listen to conversations from just one other person. The hearing impaired person has no such ability and, thus, the individual experiences a phenomenon known as a "cocktail party effect" in which all sounds are woven into an undecipherable fabric of noise and distortion. This condition is aggravated for the hearing impaired because all incoming sounds have a single point source at the output transducer of the conventional hearing aid. Under these circumstances, speech itself competes with noise and the hearing impaired person is constantly burdened with the mental strain of trying to filter out the sound he or she wishes to hear. The result is poor communication, frustration and fatigue.
Yet another performance shortcoming of the conventional hearing aid, particularly in "open mold" hearing aid fittings, resides in the area of audio feedback. The amplified signal is literally routed back to the hearing aid input microphone and passes through the amplification system repeatedly so as to produce an extremely irritating whistling or ringing. While feedback may be controlled in most fixed listening situations, it has not been controllable for the hearing aid user who faces a changing acoustic environment.
Another area of hearing impairment, related to background noise, is experienced in many noisy environments. These environments include industrial locations, office areas, computer rooms, airport pad locations, to name just a few. In these environments, even persons with so-called "normal" hearing may experience difficulty in understanding and/or discerning sounds, whether vocal or otherwise. That is, normal conversation is impossible and persons must shout to each other merely to be heard. Moreover, in many of these environments (especially industrial or airport locations), persons wear ear protectors to prevent damage to the ears. In fact, in some instances, such ear protection devices are mandated by law.
In these cases, a standard hearing aid is of little or no advantageous consequence, for the reasons discussed above. However, it is highly desirable to have some type of hearing enhancement device or apparatus for use in these situations for comfort, convenience and/or safety.